The overall purpose of this research is to investigate the effects of sexual behavior on the initiation of pregnancy in female mammals. Specifically, we will analyze the relationship between socio-sexual behavior and sperm transport in the female rat. There are three related aspects to this research program: On the organismic level, we will examine the effects of copulatory stimulation on the transport of sperm through the cervix and uterus and would examine some of the mediators of this effect. We would also examine the interrelationship between copulatory behavior and one of these physiological processes, uterine contractions. On the social-behavioral level, we will examine the ways in which the relationship between males influences the probability that a given male's sperm will ultimately fertilize the female's ova, and the characteristics of that fertilization. On the level of physiological mechanism, we will study the properties of the female rat's reproductive system that contribute to sperm transport and fertility. The purpose of this third area is to understand the mechanisms by which behavioral and physiological events are integrated into the orderly process by which sperm are transported from the male through the female's reproductive system. This project represents an integrated attempt to deal with one aspect of the organization and function of reproductive behavior in mammals.